Fractures at or near the proximal end portion of the femur may occur in any area of the proximal end and oftentimes occur in multiple locations. FIG. 1 illustrates a femur 10 including a fracture 12 in the proximal end portion 14 of the femur. Femur 10 includes a neck portion 16, a trochanteric portion 17, a head portion 18 and a body 20. As shown in FIG. 1, fracture 12 is located in neck portion 16 or trochanteric portion 17, between head portion 18 and the body 20. When such a fracture occurs, the lower or lesser trochanter region 22 may become comminuted into fragmented pieces 24 that are separated from proximal end portion 14 of femur 10.
One device commonly employed to stabilize and fixate a fractured proximal end of the femur with a comminuted lesser trochanter is an intramedullary nail. FIG. 2 illustrates an intramedullary nail 26 that has been inserted and fixed within femur 10 having a proximal end fracture 12. Typically, during a minimally invasive procedure, intramedullary nail 26 is inserted through proximal end 14 of femur 10 and into the medullary canal of femur 10. One or more cortical screws 30 may then be inserted through the cortical bone of one side of femur body 20, through a bore 32 extending through intramedullary nail 26 and into the cortical bone of the other side of femur body 20.
A lag screw 34 is inserted through the cortical bone and a bore 36 in the proximal end portion 38 of the intramedullary nail 26. Lag screw 34 includes a distal end portion 40 that is inserted into head portion 18 of femur 10. Distal end portion 40 of the lag screw 34 engages trabecular or cancellous bone within head portion 18 of femur 10. Distal end portion 40 of lag screw 34 may include an engaging member or members, such as threads, that engage the cancellous bone of head portion 18. After lag screw 34 has engaged head portion 18, the head portion is pulled by lag screw 34 toward neck portion 16 and body 20 of femur 10 to rejoin head portion 18 with femur 10 at fracture 12 as shown in FIG. 3.
When a patient, having an intramedullary nail implanted within a femur 10, places pressure on the affected leg, the acetabulum of the pelvic bone places outward and downward pressure on head portion 18 of the femur. Because the lesser trochanter has been comminuted and separated from the bone, the lesser trochanter region 24 is essentially void and does not provide much, if any, support to head portion 18. As illustrated in FIG. 3, the downward pressure on head portion 18 from the acetabulum may cause head portion 18 to rotate in a downward direction, as indicated by arrow A. The acetabulum may also place outward pressure on head portion 18 that may cause head portion 18 and lag screw 34 to move into an anatomically incorrect position, e.g., too far towards neck 16 and body 20 of femur 10.
Downward rotation of head portion 18 may cause the cancellous bone in the region designated as 42 of head portion 18 to press against distal end portion 40 of lag screw 34. The pressure of the cancellous bone against distal end portion 40 of lag screw 34 may cause strain and further injury to the bone in region 42, which may cause further bone fracture or injury to head portion 18. Furthermore, downward rotation of head portion 18 may cause the lower region 46 of head portion 18 to be moved toward body 20, past its anatomically correct position.
Typically, lag screw 34 is designed to allow for some degree of movement of head portion 18 relative to trochanteric portion 17 and body 20. However, the outward pressure placed on head portion 18 may cause lag screw 34 and head portion 18 to move outward, as indicated by arrow B, and in some instances head portion 18 may be pushed into trochanteric portion 17 and body 20 beyond its natural anatomical proposition. This may result in the head portion healing in an incorrect or unnatural anatomical position, which may cause lingering or prolonged pain to the patient after the fracture has healed.